Communication systems use optical fibers to carry large amounts of multiplexed information over long distances from transmit terminals to receive terminals. Most long-haul transmission lines and a substantial portion of short-haul transmission lines such as inter-office and intra-office links, local area networks ("LAN") and metropolitan area networks ("MAN") are optical and therefore, the information is carried over an optical fiber.
In a communication network, it is normally essential that signals from many transmission lines be cross-connected or switched to other transmission lines to provide flexibility and to permit traffic from one transmission line to be rerouted to diverse destinations. More specifically, switching is required in a network to provide provisioning, restoration in case of line failure, network reconfiguration, maintenance, operation, service and the like.
In general, optical cross-connect switches should be used with optical communication systems so as to maintain the speed and bandwidth advantages of using optical fiber. However, a disadvantage of using optical cross-connect switches, using current technologies, is that they are not practical when the number of input and output ports is large, as is required for most telecommunications service providers or when fast reconfiguration speeds are required. For example, typical non-mechanical optical cross-connect switches are on the order of 4.times.4, 8.times.8 or 16.times.16, whereas the typical switch needs to generally handle much larger number of input/output ports. Although a multiple stage architecture is implementable using typical optical cross-connect switches, the number of switch stages as well as the number of optical fiber interconnects between the stages become unmanageable and impractical to implement. Moreover, the cumulative loss resulting as the optical signals pass through each stage renders the optical signals unusable and requires the use of additional optical amplifiers on each side of the switch, increasing the complexity and cost of the switch.
A further drawback of optical cross-connect switches arises when the optical transmission systems of the transmit and receive terminals and the transport medium use different wavelength standards to carry the optical signals. In order to address these incompatibility issues, multiple optical to electrical and electrical to optical signal conversions are required that add both complexity and cost to the optical communication system.